1. Field of the Invention
The present invention relates to an ultrasonic transducer which incorporates a transmitter circuit and a receiver circuit and is generally designed for measuring distance to an object by measuring a period of time from transmission to receipt of an ultrasonic wave reflected from the object. More specifically, the invention relates to an ultrasonic transducer applicable to an automotive vehicle for monitoring relative dimensions, such as relative distance between a vehicle body and a road surface. Further, the invention relates to a compactly constructed ultrasonic transducer adapted for automotive use in suspension control, vehicular height control and so forth.
2. Description of the Background Art
In the recent years, there have been proposed various constructions of ultrasonic transducers for use in automotive control systems, such as suspension control, height control and so forth. For example, an automatic automotive suspension control system employing an ultrasonic transducer as a road roughness sensor has been disclosed in the U.S. Pat. No. 4,600,215, issued on July, 15, 1986, to Kuroki et al. In this reference, the ultrasonic transducer is installed on the lower surface of the vehicle body at an appropriate position and exposed to the outside of the vehicle body. Therefore, the ultrasonic sensor is usually is subject to dust, splashed water, muddy water and so forth. The ultrasonic transducer applicable for the aforementioned suspension control system has been disclosed in "Nissan Technical Report" No. 20, pages 98 to 101.
In addition, the dust- and water-proofing construction of the ultrasonic transducer has been disclosed in "National Technical Report" Vol. 29, No. 3, pages 144 to 147, the Japanese Utility Model First (unexamined) Publication (Jikkai) Showa 59-166599, and the Japanese Utility Model First Publication (Jikkai) Showa 59-164298.
Such ultrasonic tranducers have relatively low resonation frequency, e.g. 40 KHz. This causes echo vibration when the ultrasonic wave is generated in the ultrasonic transducers. The echo vibration caused in the ultrasonic transducer apparently interferes with acurate measurement of the distance. In order to avoid this, it is conventional construction of a road roughness sensor to have composed of separately installed ultrasonic transducers, one of which serves as an ultrasonic wave transmitter and the other of which serves as an ultrasonic wave receiver. This makes the road roughness sensor bulky and causes difficulty in installation on the under-surface of the vehicle body. Furthermore, since the conventional road roughness sensor requires two ultrasonic transducers, it results in relatively high costs.